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Conodonts, the spiky phosphatic remains (bones and teeth composed of calcium phosphate) of tiny marine animals that probably appeared about 520 million years ago, were once among the most

(5)

controversial of fossils. Both the nature of the organism to which the remains belonged and the function of the remains were unknown. However, since the 1981 discovery of fossils preserving not just the phosphatic elements but also other remains

(10)

of the tiny soft-bodied animals (also called conodonts) that bore them, scientists' reconstructions of the animals' anatomy have had important implications for hypotheses concerning the development of the vertebrate skeleton.

(15)

The vertebrate skeleton had traditionally been regarded as a defensive development, champions of this view postulating that it was only with the much later evolution of jaws that vertebrates becamepredators. The first vertebrates, which were soft-

(20)

bodied, would have been easy prey for numerous invertebrate carnivores, especially if these early vertebrates were sedentary suspension feeders. Thus, traditionalists argued, these animals developed coverings of bony scales or plates, and teeth were

(25)

secondary features, adapted from the protective bony scales. Indeed, external skeletons of this type are common among the well-known fossils of ostracoderms, jawless vertebrates that existed from approximately 500 to 400 million years ago.

(30)

However, other paleontologists argued that many of the definitive characteristics of vertebrates, such as paired eyes and muscular and skeletal adaptations for active life, would not have evolved unless the

(35)

first vertebrates were predatory. Teeth were more primitive than external armor according to this view, and the earliest vertebrates were predators.

The stiffening notochord along the back of the body, V-shaped muscle blocks along the sides,

(40)

and posterior tail fins help to identify conodonts as among the most primitive of vertebrates. The lack of any mineralized structures apart from the elements in the mouth indicates that conodonts were more primitive than the armored jawless fishes such as the

(45)

ostracoderms. It now appears that the hard parts that first evolved in the mouth of an animal improved its efficiency as a predator, and that aggression rather than protection was the driving force behind the origin of the vertebrate skeleton.

(Book Question: 514)According to the passage, the anatomical evidence provided by the preserved soft bodies of conodonts led scientists to conclude that A. conodonts had actually been invertebrate carnivores B. conodonts' teeth were adapted from protective bony scales C. conodonts were primitive vertebrate suspension feeders D. primitive vertebrates with teeth appeared earlier than armored vertebrates E. scientists' original observations concerning the phosphatic remains of conodonts were essentially correct

(Book Question: 515)The second paragraph in the passage serves primarily to A. outline the significance of the 1981 discovery of conodont remains to the debate concerning the development of the vertebrate skeleton B. contrast the traditional view of the development of the vertebrate skeleton with a view derived from the 1981 discovery of conodont remains C. contrast the characteristics of the ostracoderms with the characteristics of earlier soft-bodied vertebrates D. explain the importance of the development of teeth among the earliest vertebrate predators E. present the two sides of the debate concerning the development of the vertebrate skeleton

(Book Question: 516)It can be inferred that on the basis of the 1981 discovery of conodont remains, paleontologists could draw which of the following conclusions? A. The earliest vertebrates were sedentary suspension feeders. B. Ostracoderms were not the earliest vertebrates. C. Defensive armor preceded jaws among vertebrates. D. Paired eyes and adaptations for activity are definitive characteristics of vertebrates. E. Conodonts were unlikely to have been predators.

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29 Jun 2017, 21:09

3

1

Please comment on answer as I have not purchased OG to double check my reasoning.

Tone: EvaluateOrganization:P1: Describe the significance of a discovery that led to some hypotheses.P2: Describe 2 hypotheses - traditionalists view and paleontologists view. Authors seems to favor paleotologists' view.

Topic: Discovery of fossilsScope: Development of vetebrate skeleton based on discovery.

1. DUncertain between choice B and D.B. conodonts' teeth were adapted from protective bony scalesThus, traditionalists argued, these animals developed coverings of bony scales or plates, and teeth were secondary features, adapted from the protective bony scales.

D. primitive vertebrates with teeth appeared earlier than armored vertebrates The lack of any mineralized structures apart from the elements in the mouth indicates that conodonts were more primitive than the armored jawless fishes such as the ostracoderms.

Remarks: Is it always the case that the credited answer is what the author actually intends to support? I finally choose E because the whole passage are gears towards paleontologist view and traditionalists view is just for evaluation, that is, initially it was thought, then (MAIN CONCLUSION).Furthermore, there is the word indicate which can be concluded as conclude in this case?

2. E present the two sides of the debate concerning the development of the vertebrate skeletonUncertain between A and E.A. It does actually use findings to support each argument.E. It is mainly about presenting 2 different view using the same evidence?

Remarks:Chosen E because it encompasses 2 views and is more general. Usually function question does not include details in the answer.

3. B. Ostracoderms were not the earliest vertebrates.The lack of any mineralized structures apart from the elements in the mouth indicates that conodonts were more primitive than the armored jawless fishes such as the ostracoderms.

Although I have obtained all credited answer ,but I did not complete in the recommended time.

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01 Jul 2017, 02:51

2

The passage was easy , but the inference for question 1 was tough .If we read passage carefully we can find the answer to this question, easily.Reading the following lines reveals that primitive vertebrates with teeth appeared earlier than armored vertebratesHence D is the answer.Teeth were moreprimitive than external armor according to this view,and the earliest vertebrates were predators._________________

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01 Jul 2017, 04:52

how do I find information to answer the first question?

Okay, now I got it. Lesson: right answers can be found in any paragraph.A is too extreme because of "actually had been"E is out because no information foundC is wrong because 1/ too extreme, not all cocodonts 2/ by definition in the first paragraph, concodont is just remains, not animals

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17 Aug 2017, 19:52

[quote="anje29"]Official explanation is here

Thanks! Although I feel confused reading this OG explanation about Q1..It mainly talked about P3 when the right answer lies in P2.. [Thus, traditionalists argued, these animals developed coverings of bony scales or plates, and teeth were secondary features, adapted from the protective bony scales. ]

I may have to give up this question because I still can't find any reason to locate that answer in that position...unless you decide to look through all the passage .

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28 Aug 2017, 09:19

Valhalla wrote:

Please comment on answer as I have not purchased OG to double check my reasoning.

Tone: EvaluateOrganization:P1: Describe the significance of a discovery that led to some hypotheses.P2: Describe 2 hypotheses - traditionalists view and paleontologists view. Authors seems to favor paleotologists' view.

Topic: Discovery of fossilsScope: Development of vetebrate skeleton based on discovery.

1. DUncertain between choice B and D.B. conodonts' teeth were adapted from protective bony scalesThus, traditionalists argued, these animals developed coverings of bony scales or plates, and teeth were secondary features, adapted from the protective bony scales.

D. primitive vertebrates with teeth appeared earlier than armored vertebrates The lack of any mineralized structures apart from the elements in the mouth indicates that conodonts were more primitive than the armored jawless fishes such as the ostracoderms.

Remarks: Is it always the case that the credited answer is what the author actually intends to support? I finally choose E because the whole passage are gears towards paleontologist view and traditionalists view is just for evaluation, that is, initially it was thought, then (MAIN CONCLUSION).Furthermore, there is the word indicate which can be concluded as conclude in this case?

2. E present the two sides of the debate concerning the development of the vertebrate skeletonUncertain between A and E.A. It does actually use findings to support each argument.E. It is mainly about presenting 2 different view using the same evidence?

Remarks:Chosen E because it encompasses 2 views and is more general. Usually function question does not include details in the answer.

3. B. Ostracoderms were not the earliest vertebrates.The lack of any mineralized structures apart from the elements in the mouth indicates that conodonts were more primitive than the armored jawless fishes such as the ostracoderms.

Although I have obtained all credited answer ,but I did not complete in the recommended time.

Regarding Q2 : E. present the two sides of the debate concerning the development of the vertebrate skeletonPara 2 only present one side of the debate. The other side is presented in para 3. Then how come E is correct?

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For question 3, although I marked the correct option for Q3, I was confused between B and D. Can you help to explain how to eliminate option D?

It can be inferred that on the basis of the 1981 discovery of conodont remains, paleontologists could draw which of the following conclusions?A. The earliest vertebrates were sedentary suspension feeders.B. Ostracoderms were not the earliest vertebrates.C. Defensive armor preceded jaws among vertebrates.D. Paired eyes and adaptations for activity are definitive characteristics of vertebrates.E. Conodonts were unlikely to have been predators.
_________________

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The vertebrate skeleton had traditionally beenregarded as a defensive development, champions ofthis view postulating that it was only with the muchlater evolution of jaws that vertebrates becamepredators. The first vertebrates, which were soft-(20)bodied, would have been easy prey for numerousinvertebrate carnivores, especially if these earlyvertebrates were sedentary suspension feeders.Thus, traditionalists argued, these animals developedcoverings of bony scales or plates, and teeth were(25)secondary features, adapted from the protectivebony scales. Indeed, external skeletons of thistype are common among the well-known fossils ofostracoderms, jawless vertebrates that existed fromapproximately 500 to 400 million years ago.(30)However, other paleontologists argued that many ofthe definitive characteristics of vertebrates, such aspaired eyes and muscular and skeletal adaptationsfor active life, would not have evolved unless the(35)first vertebrates were predatory. Teeth were moreprimitive than external armor according to this view,and the earliest vertebrates were predators.

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05 Dec 2017, 07:01

pikolo2510For this one, I think D from this from (30) However, other paleontologists argued that many ofthe definitive characteristics of vertebrates, such aspaired eyes and muscular and skeletal adaptationsfor active life, would not have evolved unless the(35)first vertebrates were predatory. >> Only here to support that first vertebrate were predatory but does not draw the conclusion of paleontologists. You agree?
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Updated on: 14 Mar 2018, 23:19

With reference to question number 1, the passage says, "Thus, traditionalists argued, these animals developed coverings of bony scales or plates, and teeth were secondary features, adapted from the protective bony scales." And by "these animals", the passage clearly refers to "The first vertebrates, which were soft-bodied", which are the conodonts. Thus, we can conclude from the passage that the teeth of the conodont were adapted from protective bony scales.

So, why cant B be the correct option?

Originally posted by aviejay on 14 Mar 2018, 22:51.
Last edited by aviejay on 14 Mar 2018, 23:19, edited 1 time in total.

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15 Mar 2018, 17:06

aviejay wrote:

With reference to question number 1, the passage says, "Thus, traditionalists argued, these animals developed coverings of bony scales or plates, and teeth were secondary features, adapted from the protective bony scales." And by "these animals", the passage clearly refers to "The first vertebrates, which were soft-bodied", which are the conodonts. Thus, we can conclude from the passage that the teeth of the conodont were adapted from protective bony scales.

So, why cant B be the correct option?

Quote:

(Book Question: 514)According to the passage, the anatomical evidence provided by the preserved soft bodies of conodonts led scientists to conclude thatA. conodonts had actually been invertebrate carnivoresB. conodonts' teeth were adapted from protective bony scalesC. conodonts were primitive vertebrate suspension feedersD. primitive vertebrates with teeth appeared earlier than armored vertebratesE. scientists' original observations concerning the phosphatic remains of conodonts were essentially correct

This is a sneaky one... indeed, the traditionalists would agree with choice (B). But the anatomical evidence provided by the preserved soft bodies of conodonts cause scientists to question the traditional views:

Quote:

since the 1981 discovery of fossils preserving not just the phosphatic elements but also other remains of the tiny soft-bodied animals (also called conodonts) that bore them, scientists' reconstructions of the animals' anatomy have had important implications for hypotheses concerning the development of thevertebrate skeleton.

So now we have to consider the new evidence, which is NOT phosphatic (i.e. not the bones and teeth). This new evidence includes paired eyes, muscular adaptations for active life, the stiffening notochord along the back of the body, V-shaped muscle blocks along the sides, and posterior tail fins. The evidence from these non-phosphatic remains suggests that conodonts actually came BEFORE the armored jawless fishes such as the ostracoderms.

In other words, in light of the new evidence, other paleontologists argued that "teeth were more primitive than external armor." This new theory contradicts that of the traditionalists and the statement in choice (B). Thus, (B) should be eliminated.
_________________

Need an expert reply?Hit the request verbal experts' reply button -- and please be specific about your question. Feel free to tag @GMATNinja and @GMATNinjaTwo in your post. Priority is always given to official GMAT questions.

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13 Jun 2018, 09:37

Hi Abdur,

I really appreciate your effort in posting RCs and other verbal questions but I noticed one thing that you also mentions the line numbers in the RC. GMAT does not do that now in the real exams. So I request you to please do not mention the line numbers as they distract me.